This invention relates to an improved support system for the conducting members of the stator of a dynamoelectric machine and more particularly it relates to an integral end turn support framework for a generator which is free to move axially as the stator windings expand and contract thermally.
The end turns of a dynamoelectric machine stator are the projecting portions of the armature bars that extend outwardly from longitudinal stator slots. The end turns are necessary in order to reverse the direction of the armature bar and to circumferentially displace the end of the bar so that it can enter a slot almost 180 degrees from the slot from which it emerged. The end turns must also diverge radially from the stator axis in order that they will not obstruct the rotor of the dynamoelectric machine that is turning in the stator bore. Consequently, the stator end turns assume a rather complicated configuration in that they are skewed with respect to the stator axis and lie generally tangentially about a frusto-conical surface of revolution concentric with the stator axis. When there are two separate armature bars in each slot, these being known as “top” (radially inner) and “bottom” (radially outer) bars, one practice is to bend the top bars so that they lie tangentially in one direction about this frusto-conical surface and to bend the bottom bars in the opposite tangential direction about the surface of revolution. The matter is further complicated by the fact that, although the top and bottom bars are closely adjacent at the location where they emerge from the slot, they must spread radially with respect to one another as they move away from the stator so that space will be afforded for a series loop connecting a top bar to a bottom bar.
With this background in mind, it will be appreciated that there are many difficulties in devising a suitable structure for supporting the insulated armature bars in the end turn region. The problem has become more acute with the advent of higher operational temperatures in machines, resulting in longer thermal expansion of the stator bars and the associated stresses of this thermal expansion in the structure. Substantial heat is generated by the passage of electric current through the armature bars and, even though effective gas or liquid cooling of the bars is provided, the thermal expansion and contraction of the bars with respect to the stator slots containing them will tend to move the end turns apart in an axial direction with respect to the longitudinal center of the stator.
One support method which has been used extensively to give the strength, yet the yieldability, required of an end winding support system has been to lash the projecting armature bars to a series of circumferential support “hoops.” With this method, each bar is individually tied to a circumferential hoop with a strong flexible cord, such as glass cord impregnated with an adhesive such as epoxy resin. In a typical construction, there may be upwards of 72 (or more) top bars and bottom bars to be lashed to the circumferential hoops in the structure at either end of the stator.
In addition to separately securing the armature bars to a support structure with the foregoing method, they must be separated and secured with respect to one another. One method for accomplishing this is to use spacer blocks that conform to the space and are lashed to the armature bars. Connection rings are typically blocked in a similar fashion and tied using adhesive impregnated glass ties to ensure structural rigidity in the axial direction.
In many support structures the connection rings are securely attached to the stator frame and cannot move relative to the stator winding as it thermally grows. This can result in distortion of the electrical connection between the connection rings and the stator bars, or excessive forces being applied to the blocking components. This distortion/force can cause damage to the stator winding over the long-term operation of the machine.
The number of connection rings has increased in high output machines as the number of circuits has increased from one to two and now three or more winding circuits are used in the machine. This increases the banks of rings in the machine and makes installation of the rings more time consuming and more difficult to secure the rings and associated blocking because access to the components is more difficult as the number of banks of rings increases.